Precision parallel mechanical float

ABSTRACT

Precision parallel mechanical float for compliance automation gaging, parts handling, assembly and other operations involving a combination of tolerance misalignment. Parallel plates separated by three precision resiliently preloaded flat end rods provide resilient yield in a parallel plane as well as tilting under predetermined loading together with automatic recentering through restoring spring bias.

This is a continuation of application Ser. No. 06/941,679, filed on Dec.15, 1986, U.S. Pat. No. 4,803,706.

BACKGROUND OF THE INVENTION

In automatic gaging, assembly and parts handling operations wheremisalignment arising from tolerance variations involves a requirementfor compliance or float between the tool and its fixed or programmablemounting, various approaches have been made in the prior art. Forexample, parallel plates in the form of a thrust bearing with ballcarrier and coil spring return have been commercially sold under thetrade name "Diatest". The "Aztec Accommodator" provides multi-axiscompliance or float for automatic assembly machines using a set of sixelastomeric shear pads which compensate for machine and toolmisalignment as well as part to part variation. A remote centercompliance device "R C C Device" provides flexibility accomplished withlaminated elastomer and metal shim elements which are stiffer incompression than in shear. Such prior art devices may not have areliable accurate home or rest position and may tend to tilt rather thanshift laterally in precision parallel relationship.

SUMMARY OF THE PRESENT INVENTION

Precision parallel mechanical float is accomplished in the presentinvention through employment of three or more rods extending between abase and movable member with piloted fasteners and bias springspermitting parallel lateral float and reliable return to home or restposition. The base and movable member have essentially flat groundsurface plates that are engaged by three parallel equally spaced rodswhich are equal in length and have their ends ground flat andperpendicular with respect to their cylindrical axis.

In one embodiment, the rods are equipped with female threads at each endto facilitate the engagement of headed fasteners extending through bothplates which are held by compression springs in a manner which pilotsand loads the base and movable member on the three rods. This pilotaction enables the rods to tilt and yet remain equally spaced when alateral force sufficient to overcome the neutral home position springforce is encountered by the movable member. It moves in the direction ofthe force, but remains parallel to the base. The removal of the lateralforce permits the member to return under spring bias to its neutral homeposition. The movable member can also tilt if sufficient bending forceabout the central axis is encountered. Such tilt is limited by thecompressed height of the bias springs and free length of the pilotedfasteners.

In a second embodiment, the base and movable member are urged apart byintegral bias springs onto parallel end caps on the support rods. Thisembodiment permits over-travel and tilt toward the base and rigidengagement at the limits of the end caps away from the base, as comparedto the first embodiment which provides rigid engagement toward the base,and over-travel tilt away from the base.

Both embodiments provide preferred lateral parallel movement withprecision rest or home position within a predictable range oftranslation forces. Predeterminable translation versus tiltcharacteristics are available to the designer to achieve optimization ofinherent properties.

In a third embodiment, equally spaced rods with square ends are pilotedwithin housings extending between end plates with intermediatecircumferentially spaced extension springs creating a bias loading ofthe end plates against the rod ends.

In order to provide float head compensation for nonvertical use wheregravity-induced tilt and sag forces are encountered, the gravity weightof the gage or other tooling extending from the movable plate may bebalanced by a vertical bias spring anchored to the base and supportingthe weight of the movable plate with tooling. Counterbalancedembodiments neutralize gravity for any fixed or changing position of thebase.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially sectioned side elevation of a first embodiment;

FIG. 2 is a plan view of the FIG. 1 embodiment;

FIG. 3 is a partially sectioned side elevation of a second embodiment;

FIG. 4 is a plan view of the FIG. 3 embodiment;

FIG. 5 is a sectional side elevation of a third embodiment;

FIG. 6 is a plan view of the FIG. 5 embodiment;

FIG. 7 is a schematic side elevation diagram of rods such as employed inthe FIG. 1 and 5 embodiment in their home positions;

FIG. 8 is a view similar to FIG. 7 showing the movable member indisplaced position;

FIG. 9 is a partially sectioned side elevation of a fourth embodimenttaken along the line 9--9 of FIG. 10, wherein the compliant rods extendin a horizontal direction;

FIG. 10 is an end view of the embodiment shown in FIG. 9;

FIG. 11 is a sectional side elevation of a fifth embodiment similar tothat of FIG. 9 illustrating a counterbalance for the cantilever load onthe movable member;

FIG. 12 is a sectional side elevation of a sixth embodiment similar tothat of FIG. 11 illustrating a different system for counterbalancing themovable member;

DETAILED DESCRIPTION OF FIRST EMBODIMENT

With reference to FIGS. 1 and 2, base plate 10 supported on any suitablemounting 11 in turn supports movable plate 12 with gage mount 13 orother tooling secured on three columnar rods 14 equallycircumferentially spaced as shown in FIG. 2. Clearance apertures 15 inplates 10 and 12 for cap screws 16 threaded into rod ends 17 retaincompression springs 18 biasing plates 10 and 12 against rod ends 17which are precision ground to equal length and squareness to establishprecise parallellism between plates 10 and 12.

Any lateral force on movable plate 12 sufficient to overcome thecombined preload of the six compression springs will cause a tilting ofthe rods, as schematically illustrated in FIG. 8, accommodated withinthe limited clearance of apertures 15. Torque compliance as well astilting compliance and extension compliance is also accommodated by thisconfiguration while compressive compliance of plates 10 and 12 towardeach other is resisted by the rods.

With reference to FIGS. 3 and 4, preloaded compression springs 20 biasplates 21 and 22 into engagement with heads 23 of rods 24, in this caseaccommodating parallel lateral float, torque, tilting and compressivecompliance while resisting extension between plates 21 and 22.

With reference to FIGS. 5 and 6, base plate 30 is separated from movableplate 31 by three circumferentially spaced rods 32 passing through baseguide body 33 and upper guide body 34 secured to respective plates 30and 31 by intermediate screws 35. Rod passages 36 within the guide bodylimit relative lateral float while "O" rings 37 in counterbored pocketsat either end assure accurate return to a central home position uponrelease of any lateral load under the bias of three tension springs 38spaced circumferentially between the three rods 32. Cross pins 39 inrespective counterbores at the ends of spring passages through bodies 33and 34 serve to anchor the ends of extension springs 38 which return andretain the operative gage assembly for which this embodiment is employedin its neutral position as shown.

With reference to FIGS. 9 and 10, a means for supporting the gravityload of a floating mounting plate 40 from a base plate 41, havinghorizontal rods 42 biased in tension by compression springs 43, isprovided by adjustable leaf spring 44 anchored at 45 to base plate 41.In this case, the three pairs of axially aligned rods are retained incentered alignment by screw 44b engaging threaded holes in the ends.Rubber boot 45 is clamped to respective plates 40 and 41 by strap clamps46 as a dirt seal.

When a float head is used in nonvertical position, as in the case of theFIG. 9 embodiment, the gravity weight of the head, when its center islaterally displaced from support point 47, creates an unbalanced momenttending to tilt the head which necessitates relatively higher strengthcompression springs 43 than would otherwise be required to resist suchtilting. In addition, an unequal force is required in upward deflectionas compared to downward deflection since it would take more force tolift the gage tip than to force it down.

A solution for stationary nonvertical use is illustrated in FIG. 11where the addition of a rearward projecting extension 50 under themovable member 51 shifts the center of gravity 52 to a position directlyover contact 53 of vertical bias spring 54 which may be accuratelyadjusted by counterweight 55. This permits system float in alldirections without preload tilting force and with biasing springs, inthis case illustrated schematically as extension springs 56, of lightstrength equal to float springs employed with a vertical gage.

With reference to FIG. 12, a general solution to balance nonverticalapplications of the float head in any orientation is illustrated whereina central lever 60 is provided with a spherical fulcrum 61 seated instationary member 62 and a spherical end 63 supporting the movablemember at its center of gravity and is counterbalanced by adjustableweight 64 so that gravity forces will be compensated in all positionswithout the use of springs. Accordingly, only the effective restoringforce from any displacement will be variable, and again the springbiasing forces for accommodating float may be calibrated to the desiredrequirements of the application.

In all embodiments, the ratio of rod diameter and length, together withspring preload determine basic resistance to lateral displacement whilethe effective spacing of rods together with spring preload determine theresistance to tilting forces which are offset from the movable plateengaged by the rods. It will be understood that desired respectivevalues for accommodating the parallel float and tilting may beindividually determined and adjusted by the design choice of the ratiosof rod diameter to length and to rod separation; thus, resistance toparallel float may be reduced to any desired value by reduction in roddiameter without substantially changing resistance to tilt; whiledesired resistance to tilt may be increased through increasing springpreload for any given spacing of rods.

It will also be understood that for all embodiments, as long as tiltforces are resisted, any lateral shifting of the movable member will beaccommodated with precision parallel relation and automatically restoredto accurate neutral position upon release of displacement load,provision being made for retention of the rod ends in requiredorientation.

With reference to FIG. 7, spring loading plus gravity centered at F₁will resist tilting force applied at F₂ until F₂ ×L exceeds F₁ ×(D÷2)and will resist lateral force applied at F₃ until F₃ ×H exceeds F₁ ×D₂.Likewise, torque will be resisted until equal and opposite forcesapplied at D₁ diameter each exceeds F₁ ÷2×D₂. Resistance forces to F₃and torque will diminish toward 0 as displacement, shown in FIG. 8,approaches D₂. Accordingly, displacement must be limited to a fractionof D₂ for a restoration force to be available.

The force diagram as applied to two columns in FIGS. 7 and 8 cansimilarly be applied to three or more column embodiments by makingappropriate geometric allowances; e.g. effective radius of tiltingrelative to effective center of force F₁.

I claim:
 1. Precision parallel float mechanism comprising a baseincluding three substantially equally spaced first registration surfacesin a fixed plane of reference, a relatively displaceable member havingthree directly opposed corresponding second registration surfaces, saiddirectly opposed corresponding second registration surfaces beingpositioned in another plane of reference parallel to said fixed plane ofreference whereby a pair of opposed registration surfaces are formedwith each first registration surface and a respective directly opposedcorresponding registration surface, three rigid columns each rigidcolumn having a pair of peripheral contact surfaces engagingrespectively a pair of said opposed registration surfaces, yieldablepreloaded resilient means establishing normal compressive peripheralcontact engagement with said first and second registration surfacessubject to each column tilting to opposite peripheral side edge contactwith respective registration surfaces in response to a predeterminedforce couple imposed on the parallel planes of reference of said baseand displaceable member, said mechanism including means for confiningsaid peripheral contact surfaces against lateral displacement relativeto said registration surfaces.